Video compression is used to compress video data for storage on devices with limited memory and transmission over communication channels with limited bandwidth. A number of video compression standards, such as MPEG-2, VC-1, and AVC compress the video data by, among other things, removing or deemphasizing higher frequency components. The higher frequency components have been observed to be less perceptible to the human eye.
However, when the compressed video data is decompressed and displayed on a display device, the video data has been observed to produce a different intensity compared to the original video data. The intensity difference is the result of the nonlinear response of system. The eye takes things with high spatial frequency and averages their intensity. When a nonlinear response is involved, this averaging changes the perceived value. For example, if a system has a response of y=x2, with the values of x, 1, 2, and 3, the output is 1, 4, and 9. If the input is low pass filtered and changed to 2, 2, and 2, the output is 4, 4, 4. In the original case, the average of the output value is 14/3 In the low pass filtered case, it is 4.
Display devices, such as CRTs, have non-linear characteristics between pixel value and brightness. To compensate for this, the displayed video data is gamma corrected. However, even where the decompressed video is perceptually similar to the original video, its response to gamma correction often produces a different intensity compared to the original video data.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.